Binding of α-tocopherylquinone, an oxidized form of α-tocopherol, to glutathione-S-transferase in the liver cytosol

alpha-Tocopherol (vitamin E) is an important fat-soluble antioxidant in biological systems and, as a result of scavenging reactive oxygen, it is converted to alpha-tocopherylquinone. alpha-Tocopherol binds to alpha-toeopherol transfer protein (alpha TTP) in the liver cytosol, whereas alpha-tocopherylquinone does not. We found that alpha-tocopherylquinone binds to a liver protein with a molecular mass of about 40 kDa that is distinct from alpha TTP. This alpha-tocopherylquinone binding protein was purified further by multiple-step column chromatography, Sodium dodecylsulfate-polyacrylamide gel electrophoresis of the final preparation yielded a single band with an apparent molecular mass of 25 kDa, which microsequencing revealed was identical to glutathione-S-transferase (GST), The GST activity was inhibited in the presence of alpha-tocopherylquinone, as it is by other nonsubstrate ligands for GST, confirming that GST and alpha-tocopherylquinone interact directly, alpha-Tocopherylquinone binds to GST and may be transported to the site of metabolism or excreted in the bile as other non-substrate ligands for CST. (C) 1998 Federation of European Biochemical Societies.